Milwaukee Road class F6

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Milwaukee Road class F6
MILW F6.jpg
Milwaukee Road class F6 locomotive #6409.
Photo by Otto Perry at Chicago, Illinois on September 23, 1930.
Type and origin
Power type Steam
Builder Baldwin Locomotive Works
Serial number 61135–61148
Build date January–March 1930
Configuration 4-6-4
UIC class 2′C2′ h2
Gauge 4 ft 8 12 in (1,435 mm) standard gauge
Leading dia. 36 in (914 mm)
Driver dia. 79 in (2,007 mm)
Trailing dia. 43 in (1,092 mm)
Loco weight 375,850 lb (170,480 kilograms; 170.48 metric tons)
Total weight 532,000 lb (241,000 kilograms; 241 metric tons)
Fuel type Coal
Fuel capacity 40,000 lb (18,000 kilograms; 18 metric tons)
Water cap 15,000 US gal (57,000 l; 12,000 imp gal)
 • Firegrate area
80 sq ft (7.4 m2)
Boiler pressure 225 lbf/in2 (1.55 MPa)
Feedwater heater Coffin flush in smokebox
Cylinders Two
Cylinder size 26 in × 28 in (660 mm × 711 mm)
Valve gear Baker valve gear
Performance figures
Tractive effort 45,820 lbf (203.8 kN)
Operators Milwaukee Road
Class F6
Number in class 14
Numbers 6400–6413; renumbered 125–138 in 1938
Delivered 1929
Retired 1952–1954
Disposition All scrapped
Milwaukee Road class F6-a
MILW F6a.jpg
Milwaukee Road F6-a locomotive #6417. Photo by Otto Perry at Chicago, Illinois on September 25, 1935.
Type and origin
Only items that differ from class F6 above are shown
Power type Steam
Builder Baldwin Locomotive Works
Serial number 61655–61662
Build date October–November 1931
Wheelbase Loco: 40 ft 9 in (12.42 m)
Height 15 ft 6 in (4.72 m)
Loco weight 380,220 lb (172,460 kilograms; 172.46 metric tons)
Feedwater heater Wilson Water Conditioner
Operators Milwaukee Road
Class F6-a
Number in class 8
Numbers 6414–6421; renumbered 142–146, 139–141 in 1938

The Milwaukee Road classes F6 and F6-a comprised twenty-two steam locomotives of the 4-6-4 configuration, commonly nicknamed “Hudson” but known as “Baltic” on the Milwaukee Road. They would have been the first 4-6-4 tender locomotives in the world were it not for the Milwaukee's financial difficulties which culminated in bankruptcy in 1925.

The fourteen class F6 locomotives were not delivered from their builder, the Baldwin Locomotive Works of Philadelphia, Pennsylvania, until 1929–1930. In 1931, eight sister locomotives of class F6-a were delivered; these differed in few aspects but can be distinguished by the straight running boards of the F6-a, in contrast to the stepped running boards of the F6.

Technical details[edit]

The 1925 design was by Milwaukee Road Chief Mechanical Engineer C. H. Bilty, with detail design by the Baldwin Locomotive Works, who actually built them. They represented the best of American locomotive practice at the time, and were given all the latest devices and fittings. A Coffin feedwater heater was fitted, which was the Milwaukee's favorite type; this was installed flush in the extended smokebox, and thus was not at all obvious. Possibly because of this, the boiler lagging was continued over the smokebox, which was not common; most North American locomotives had bare smokeboxes which were graphited, rather than painted. The associated steam-driven centrifugal water pump was located under the cab at the left rear. The class F6-a was fitted with the tender-mounted Wilson Water Conditioner instead of the Coffin feedwater heater.

Valve gear was of the low-maintenance Baker type, with (of course) power reverse. A front-end throttle was installed, with the distinctive linkage running along the boiler on the engineer's side. A mechanical lubricator, driven from the crosshead on the engineer's side, fed oil to the cylinders, valves, guides and other parts of the running gear. Many of the locomotives were fitted with a speedometer, which was attached to the engineer’s side frontmost leading axle.

A single air pump for the locomotive and train air brakes was fitted to the fireman's (left) side, with air tanks under the running boards on both sides. Like all larger North American coal-burning locomotives of the time, an automatic stoker was fitted; the two-cylinder engine to drive this was under the cab floor on the fireman's side.


Locomotive #6401 received large, "Elephant ear" smoke deflectors in 1936 as an experiment; these were kept for several years, but were not fitted to other locomotives. Later that year a sheet-steel pilot was fitted to it and several other locomotives to replace the boiler-tube pilot installed from new. This featured a swing-up coupler. As well as giving a more attractive, streamlined look, this had a serious safety aspect; a sheet-steel pilot without a protruding coupler was more likely to deflect an obstacle without catching on it in e.g. a grade crossing accident.


At first the locomotives were used mostly between Chicago and Minneapolis, but later on when the F6-a locomotives arrived they served as far west as the beginning of the electrified zone.

When delivered the class F6 were numbered 6400–6413, with the class F6-a numbered 6414–6421. At the 1938 renumbering, they were numbered 125–138 and 139–146

Table of locomotives[1]
Original No. 1938 No. Class Baldwin
serial No.
Built Retired
6400 125 F6 61135 January 1930 June 1954
6401 126 F6 61136 January 1930 December 1954
6402 127 F6 61137 January 1930 February 1954
6403 128 F6 61138 January 1930 February 1954
6404 129 F6 61139 January 1930 December 1953
6405 130 F6 61140 January 1930 December 1952
6406 131 F6 61141 January 1930 September 1952
6407 132 F6 61142 January 1930 October 1952
6408 133 F6 61143 January 1930 October 1952
6409 134 F6 61144 January 1930 July 1954
6410 135 F6 61145 January 1930 September 1954
6411 136 F6 61146 February 1930 November 1954
6412 137 F6 61147 February 1930 December 1954
6413 138 F6 61148 March 1930 December 1954
6414 142 F6-a 61655 October 1931 December 1954
6415 143 F6-a 61656 October 1931 December 1954
6416 144 F6-a 61657 October 1931 December 1954
6417 145 F6-a 61658 October 1931 December 1954
6418 146 F6-a 61659 November 1931 December 1954
6419 139 F6-a 61660 November 1931 August 1952
6420 140 F6-a 61661 November 1931 June 1954
6421 141 F6-a 61662 November 1931 October 1952

Speed record[edit]

On July 20, 1934, Milwaukee Road class F6 Baltic #6402 participated in a test run to prove the feasibility of a high-speed service, which was launched as the Hiawatha service in 1935. The test used a regular service train from Chicago, Illinois to Milwaukee, Wisconsin, train 29. This was redesignated as Second 27 just for that day and given a special, high-speed timing. With a five-car train of 840,000 pounds (380 t), #6402 completed the 85 miles (137 km) in 67 minutes and 37 seconds start to stop. The eventual Hiawatha timing was 75 minutes for this journey, and the Hiawatha timing was possibly the fastest scheduled train in the world in the 1930s.

While the ends of the trip were taken at relatively low speeds, the 68.74 miles (110.63 km) between the Chicago suburb of Mayfair and Lake, Wisconsin was completed in 45 minutes and 53 seconds, an average of 89.89 mph (144.66 km/h). Times were taken with a stopwatch as each station was passed, and in addition the locomotive was fitted with a speedometer; this recorded the speed on a chart, indicating a maximum of 103.5 mph (166.6 km/h) was reached. The fastest inter-station average speed was 95.6 mph (153.9 km/h) between Oakwood and Lake; British expert Brian Reed showed that the latter half of that was an uphill gradient and thus speeds in the first half must have been significantly higher than the overall average. He stated that:

This must be taken as the first time a U.S. steam loco topped “the hundred”.[2]

More recently, British train timer Bryan Benn has taken the gradient profile given in Brian Reed's book and shown that it supports a maximum speed in excess of 101 mph during that portion of the run. He believes this is the first claim of over 100 mph (160 km/h) for a steam locomotive in which the surviving documentation strongly indicates its accuracy, and thus that #6402 was the record holder for steam locomotive speed for at least a short time.


  1. ^ Edson 1977, p. 49.
  2. ^ Reed, p. 28.
  • Benn, Bryan, Which was the world's first genuine 100 mph steam locomotive?. Retrieved February 5, 2010.
  • Edson, William D. (Spring 1977). "Milwaukee Road All Time Steam, Diesel and Electric Roster". Railroad History. Railway and Locomotive Historical Society Inc. (136): 49. 
  • Reed, Brian (1972). Loco Profile 26 – The Hiawathas. Windsor, Berkshire, UK: Profile Publications Ltd. 
  • Westcott, Linn H. (1960). Model Railroader Cyclopedia - Volume 1: Steam Locomotives. Milwaukee, Wisconsin: Kalmbach Books. pp. 203–207. ISBN 0-89024-001-9.